The present invention relates to a mobile communication apparatus and, more particularly, to a mobile communication apparatus having a battery.
A conventional mobile communication apparatus such as a car telephone, a portable telephone, or a radio selective calling receiver uses a battery as a power supply, whose battery capacity is limited. For this reason, a digital radio apparatus or the like based on a TDMA (Time Division Multiplex Access) scheme such as the multichannel carrier scheme performs a battery saving operation to minimize the power consumption. A battery saving operation is performed as follows. In a standby state or speech communication, the reception circuit is operated only when a control signal must be received, but the supply of a current from the power supply to the reception circuit is stopped in other periods. With such a battery saving operation, the power consumption is reduced to allow the long-duration use of the apparatus.
Japanese Patent Laid-Open No. 5-22210 discloses a mobile radio communication apparatus with a long standby time. In this apparatus, when the reception electric field strength is high in a standby state, i.e., a very high reception sensitivity is not required, the reception section is controlled to lower the reception sensitivity to the required minimum reception sensitivity, thereby reducing the power consumption.
FIG. 5 shows the mobile ratio communication apparatus disclosed in this reference. A signal from a base station is received by an RF (Radio Frequency) circuit 102 of a reception section 120 through an antenna 100 and a demultiplexer 101 to be converted into a first IF (Intermediate Frequency) signal. The first IF signal is converted into a second IF signal by an IF circuit 103. The second IF signal is detected by a detector 104. The resultant signal is output to a terminal 105.
An RSSI (Received Signal Strength Indicator) circuit 107 outputs an output voltage corresponding to the amplitude of the signal output from the IF circuit 103 to a comparator 106. A reference level generating circuit 108 stores the characteristics of the RSSI circuit 107 which correspond to the reception electric field strength. The comparator 106 compares the output voltage from the RSSI circuit 107 with the output voltage from the reference level generating circuit 108, and calculates a reception electric field strength on the basis of the stored characteristics.
A control circuit 109 stores the required minimum reception sensitivity corresponding to the reception electric field strength in advance. The control circuit 109 controls the RF circuit 102 to set the required minimum reception sensitivity corresponding to the output from the comparator 106, and also performs control to correct by a change in the gain of the RF circuit 102 the characteristics stored in the reference level generating circuit 108.
Although the power consumption can be reduced to a certain degree in the above conventional mobile radio communication apparatus, a longer standby time or a longer speech communication time is required for a mobile communication system.